In the Digital Video Broadcasting over Terrestrial 2 (DVB-T2) system, data transmission is completed in the form of data frames. At a beginning of each data frame is a P1 symbol that contains certain information at a transmitting end, such as information of a fast Fourier transform (FFT) mode for data modulation and information of an antenna transceiving type for identifying multiple-input or single-input. Therefore, upon receiving a digital data stream compliant with the DVB-T2 specification, a receiver needs to first retrieve information carried in the P1 symbol in order to configure the demodulation for correctly demodulating the digital data stream.
FIG. 1 shows a schematic view of a DVB-T2 compliant digital data stream containing a P1 symbol. As shown, a data frame comprises a P1 symbol, a P2 symbol and data. The P1 symbol is mainly consisted of three data in sequence, namely a data C with 542 samples and a time length of TC, a data A with 1024 samples and a time length of TA, and a data B with 482 samples and a time length of TB. Further, the data C is a frequency-shifted data generated by performing frequency shifting upon a first half of the data A (i.e., a data C′), and the data B is a frequency-shifted data generated by performing frequency shifting upon a second half of the data A (i.e., a data B′). An equation for the P1 symbol p1(t) is as follows:
            p      1        ⁡          (      t      )        =      {                                                                      p                                  1                  ⁢                  A                                            ⁡                              (                t                )                                      ⁢                          ⅇ                              ⅈ                ⁢                                                      2                    ⁢                    π                                                        1024                    ⁢                    T                                                  ⁢                t                                                                          0            ≤            t            <                          542              ⁢                                                          ⁢              T                                                                                      p                              1                ⁢                                                                  ⁢                A                                      ⁡                          (                              t                -                                  542                  ⁢                  T                                            )                                                                          542              ⁢              T                        ≤            t            <                          1566              ⁢              T                                                                                                      p                                  1                  ⁢                  A                                            ⁡                              (                                  t                  -                                      1024                    ⁢                    T                                                  )                                      ⁢                          ⅇ                              ⅈ                ⁢                                                      2                    ⁢                    π                                                        1024                    ⁢                    T                                                  ⁢                t                                                                                        1566              ⁢              T                        ≤            t            <                          2048              ⁢              T                                                            0                                      otherwise            ,                              where P1A is content of the data A, and T is a sampling cycle of the digital data stream.
Since the data C and B are frequency-shifted data respectively generated by performing frequency shifting upon a part of the data A, correlation between the data C and B and the data A may be looked into to determine whether a currently received data is the P1 symbol. In addition, by comparing correlation between the data C and B and the data A, a location of the P1 symbol may be identified to correctly retrieve the P1 symbol from the digital data stream. However, identifying a location of the P1 symbol from the digital data stream is quite a challenging task, and errors may result in subsequent data demodulation based on an incorrect location of the P1 symbol.